Improvements to the Wankel rotary engine to permit operation with heavy fuels have been attempted. Direct injection, stratified charge, and prechambers have been used in rotary engines to permit operation with heavy fuels. A prechamber may be located in the engine housing, separate from the main chamber. Fuel ignited in the prechamber is then flashed into the working chamber, in order to ignite the main fuel charge.
High compression ratios have been employed to achieve proper functioning of diesel powered internal combustion engines. In compression-ignition systems, the diesel fuel is ignited by the heat of compression alone, with compression ratios typically of between about 14:1 to about 20:1. Due to the geometry of a rotary engine, high compression ratios are impractical to attain. While it is possible to design the geometry of the engine to attain a high compression ratio, rotary engines of this type have not been successful. For instance, to provide a sufficiently high compression ratio, the geometry is modified so that it is long and narrow, which results in small displacement for the size of the engine. In addition, high compression ratios in rotary engines cause high mechanical loads requiring heavy components. This defeats the major size and weight advantage the engine has over piston engines.
Attempts to design a rotary engine operating on the compression-ignition principle have resulted in complex designs, none of which have achieved commercial practicality. For example, in U.S. Pat. No. 3,957,021 to Loyd, a compressor is used to supply a separate air charge into the prechamber in order to initiate combustion. The compressor adds cost and complexity to the engine design. Moreover, compressed air must be released at timed intervals, thus further complicating matters. Similarly, U.S. Pat. No. 4,091,789 to Jones discloses a stratified charge rotary engine requiring two injectors and a timed spark ignition source. This engine operates at relatively low compression ratios but requires two timed injectors per rotor and a timed electrical spark.
A rotary engine is advantageous because of its size, weight, and relative simplicity. A commercially practicable heavy fuel rotary engine would have applicablity wherever low volatility fuel is an advantage or where unthrottled operation yields a thermal efficiency advantage.
Thus, there is a need in the art for a rotary engine which achieves stable combustion of heavy fuel at relatively low compression ratios. Similarly, there is a need in the art for a practical Wankel rotary engine with a relatively low compression ratio, which will achieve consistent ignition of the fuel/air charge using direct fuel injection, without requiring complex auxiliary components.